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Engineering GraphicsORTHOGRAPHIC ople who work with drawings develop the ability to look at lines on paper or on a computer screen and"see" the shapes of the objects the lines represent. Visualization is an essential skill when working with technicalinformation. Architects, engineers, machinists, carpenters, welders, installers -- many types of workers createor use drawings. Technical drawings and sketches provide a clear, concise, exact method of representingthree-dimensional information. Starting at the Industrial Revolution the process and theory of technical drawinghas evolved into a universal graphical language.CopyrightedMaterialHow do people who work with drawings think about the lines they see? What is the mental process that allowsskilled workers to quickly interpret abstract lines, curves and shapes to form an exact mental image of theobjects represented? Part of the answer is that these people rapidly recognize and analyze basic types of surfaces.Once individual surfaces are recognized, then the interfaces -- common edges and intersections -- between thesurfaces may be visualized. With practice this process becomes very rapid.In the next four chapters much emphasis will be placed on recognizing types of plane and curved surfaces inspace. Only three types of plane (flat) surfaces exist. Many types of curved surfaces -- cylinders, cones, spheres,torus, etc. -- exist. By recognizing each type of surface, rules may be applied to the appearance of the surfaceon drawings. Visualizing objects is a process of assembling the individual surfaces into shapes then into objects.Portions may be solved by following rules before the actual answer is apparent. Objects may be solved in muchthe same way a mathematical expression is solved.CopyrightedMaterialLearning to visualize objects is an individual skill. Making clay models, computer models or LEGO (tm) modelsis an excellent step. Seeing the answer from someone else destroys all chance to learn. Problems at the end ofeach chapter are designed to develop visualization skills. Work on each problem for short time. If the answeris not apparent, come back to the problem later.D-1

ORTHOGRAPHIC PROJECTIONEngineering GraphicsPictorial vs. Orthographic ViewsCopyrightedMaterialPictorial drawings give quick three-dimensionalviews of objects. They are often used for advertising, repair manuals, and general information.Shapes are easier to visualize and intersections ofsurfaces can be seen.Pictorials distort the lengths of lines and anglesat corners. These drawings cannot be used forproduction.This drawing is an isometric pictorial.CopyrightedMaterialProduction (detail) drawings describe the shape ofthe object by looking directly at the faces of theobject. In this way the true length lines and trueangles at corners may be seen. Multiple views areneeded. These views are two-dimensional. Viewsare obtained by looking in the direction of thearrows shown in the isometric above.Multiple views are needed. FRONT, TOP andRIGHT SIDE views are used here.CopyrightedMaterialDimensions and notes give size and manufacturinginstructions. Dimensions are placed where theshape shows best.Engineers, architects and designers "see" objects inpictorial mental images. They must convert pictorial ideas into orthographic form for production.Workers and others must convert the orthographicdrawings back into pictorial images in order toanalyze the shapes and use the information. Thetransition from pictorial - to orthographic - to pictorial is a constant process.CopyrightedMaterialBy far, the most difficult step is converting orthographic drawings to pictorials. This process requires looking at two-dimensional images to getthree-dimensional shapes.Computer modeling is simplifying this process.D-2

Engineering GraphicsORTHOGRAPHIC PROJECTIONMultiple View DrawingsCopyrightedMaterialOrthographic views may be obtained by placing an object inside a "glass box". Faces of thebox are at right angles. Surfaces on the objectare aligned parallel to the faces of the box whenpossible. Views are drawn by projecting linesand surfaces to each face of the box.Orthographic views are two-dimensional.In the front view there is no way to show thedifference in level (depth) between the surfaces.CopyrightedMaterialProjection planes of the glass box are perpendicular to each other. Three regular planes areshown. Left side, bottom and back planes mayalso be used.These planes are also used by computer graphics systems.CopyrightedMaterialThe line of sight for each view is perpendicularto each projection plane. Looking perpendicularto a plane gives the true size of the plane in aparticular view -- the other projection planesappear in edge-view.Surface 1,2,3,4 is parallel to the front projectionplane. It will appear as a surface (true size) inthe front view.In the top view 1,2,3,4 appears as edge-ofsurface A-B.CopyrightedMaterialIn the side view 1,2,3,4 appears as edge-of-surface C-D."Reading" orthographic views involves integrating this type of information about everysurface on the object to form a mental image.D-3

ORTHOGRAPHIC PROJECTIONEngineering GraphicsSix Regular Orthographic ViewsCopyrightedMaterialSix regular views of an object may be projected.Rule: Each feature of an object must beshown as visible lines in at least one view.Drafters must decide which views to draw.Sometimes additional (auxiliary) views areneeded to clarify shapes and remove ambiguities. Dimensions, for example, must beplaced on the "true shape" views. Partialviews may be drawn.CopyrightedMaterialNotice the hinge locations when unfoldingthe plastic box. Observe the alignment of theviews: front-top-bottom, and front-rightleft-back. Views must be placed on the pageor computer screen in this form.This graphic shows the AMERICANSTANDARD ARRANGEMENT OFVIEWS. Third Angle ProjectionViews must be sketched or drawn according to this alignment.CopyrightedMaterialPeople who work with drawings expect to find the views of objects in thisform.Front, top and bottom views must bealigned vertically. All corners and features must project vertically.Front, right side, left side and backviews must be aligned horizontally.Features and corners must project horizontally.CopyrightedMaterialMetric Drawings - First Angle ProjectionDrawings made according to metric standards may place the views in a different form on the page.See page D- 20 for an explanation.D-4

Engineering GraphicsORTHOGRAPHIC PROJECTIONOrthographic Views are Two-DimensionalCopyrightedMaterialSurfaces on an object are at different levels.A is more to the front, then B, then CD is more to the top, then EF is more to the right, G is more to the left.If a line separates two surfaces, there must bea difference in level between the surfaces.CopyrightedMaterialWhen surfaces A, B and C are projected to thefront projection plane, they appear next to eachother. Depth is lost. The person reading thedrawing must look at an adjacent (top or side)view to see which surface is in front.CopyrightedMaterialWhen F and G are projected to the side view, theyappear next to each other. Width is lost. Thesurfaces are at different levels. Look at the frontor top views to see which surface is more to theright or left.CopyrightedMaterialD and E appear next to each other in the top view.Height is lost. Look at the front or side views tosee which surface is higher and which surface isset down lower.D-5

ORTHOGRAPHIC PROJECTIONEngineering GraphicsCommon Dimensions Between ViewsCopyrightedMaterialMajor dimensions for objects are commonly namedHEIGHT, WIDTH AND DEPTH. Orthographicviews are two-dimensional so each view can showonly two of the three dimensions.In any two adjacent views, all three dimensionsmay be seen.WIDTH is the common dimension between thefront, top (and bottom) views.Top view shows width and depthFront view shows width and height.CopyrightedMaterialWidth is projected vertically between the views.HEIGHT is the common dimension between thefront, right side, (left side and back) views.Front view shows height and widthSide view shows height and depth.Height is projected horizontally betweenviews.theCopyrightedMaterialDEPTH is the common dimension between the topand side views. While DEPTH is measured in ahorizontal direction in space, it must be measured ina vertical direction in the top view.Side view shows depth and heightTop view shows depth and width.CopyrightedMaterialDepth is measured horizontally in the side viewand vertically in the top view.D-6

Engineering GraphicsORTHOGRAPHIC PROJECTIONTransferring the DEPTH DimensionCopyrightedMaterialSeveral methods of transferring depth are shown. Dividers are the quickest and most accurate tool. Use thepaper method for plain paper sketches.CopyrightedMaterialCopyrightedMaterialA miter line may be used to geometrically transferdepth from the side-to-top and the top-to-side views.This technique is used on drawings created with Tsquares or drafting machines. This technique may beused to transfer depth measurements on computerdrawings.CopyrightedMaterialThe miter line technique may be used on two dimensional CAD drawings.D-7On grid papers,count the "units" totransfer depth.

ORTHOGRAPHIC PROJECTIONEngineering s are shown in standard arrangement. Notice the common dimensions between the views. Also, note theline of sight between the views. For example, the arrow shows the direction to look at the front view to get theside view. And, the direction to look at the side view to get the front view.CopyrightedMaterialActually holding an object and turning it asshown will help verify the views and theprojection theory on previous examples. Besure you turn the object correctly to draweach view. At first people tend to draw someviews backward!Clay ModelsCarving clay models of objects is the mosteffective way to experience the transitionfrom real objects to paper drawings. Creatingmodels from drawings will strongly reinforcethe transition from abstract lines on paper toreal objects.CopyrightedMaterialStyrofoam packing blocks also make goodmodeling material.D-8

Engineering GraphicsORTHOGRAPHIC PROJECTIONVisualizing ObjectsCopyrightedMaterialCarving models (or just thinking through the steps) is an effective way to visualize objects. Starting with a solid block, observe the outlines of the top, front and side views. Cut awaymaterial from the object to leave the profiles shown.No material is left in the open areas. This means that the objectmust be cut all the way across: top to bottom, front to back, rightto left respectively.CopyrightedMaterialFrom the front view, cut away the block as shown. Thiscut creates surfaces A and B.line 1,2 is added to the top viewline 9,10 is added to the side view.CopyrightedMaterialIn the top view, remove the block shown. This createssurface C.Hidden line 1,2 is added to the front view.Lines 3,6 and 5,4 are added to the side view.A similar process is used in computer solids modeling."Tools" are shaped then mathematically subtractedfrom an object.CopyrightedMaterialCut the block from the top of the object. This completesthe shape outlined in the first picture.Surface D is createdline 1,2 is added to the front viewline 3,4 and 5,6 are added to the top view.D-9

ORTHOGRAPHIC PROJECTIONEngineering GraphicsBuilding Objects by Joining SolidsCopyrightedMaterialObjects may be visualized by imagining the basic shapeswhich were joined.Basic shapes include:conesrectangular rialPieces include cylinders and plates in this example.CopyrightedMaterialObjects are often combinations of added shapes minus subtractedshapes.These concepts are used in computer solids modeling. Librariesof shapes may be provided which generate geometric solids. Thesolids may then be added together (union) or subtracted away.CopyrightedMaterialTwo rectangular solids are first joined together, then a cylinder issubtracted to create the final shape.D - 10